1. Field of the Invention
The present invention relates generally to magnets and in particular to an improved magnetic decoupler for use with antitheft devices, in which the magnetic decoupler comprises a plurality of magnets arranged with their magnetic orientations orthogonal to each other.
2. Description of the Related Art
With reference to FIGS. 5 and 6, a known antitheft device used, for example, in retail sales stores that sell such goods as clothing or dry goods comprises a security tag, or simply, tag, usually having the shape of a disk or other generally planar shaped object. The tag contains a proprietary material that sets off an alarm, for example, if the goods are removed from the store without first detaching the tag. The tag is commonly attached to the goods by means of a tapered pin. The pin is inserted through the goods and into one side of the tag. The length of the pin is generally greater than the thickness of the tag. The side of the tag opposite that into which the pin is inserted is provided at its center with a nipple that accommodates the pin, so that the full length of the pin can be inserted into the tag. The pin may have one or more circumferential grooves. The nipple contains a mechanism for gripping the pin, or engaging a groove in the pin, and is constructed so that the pin can be easily inserted into the nipple, but once inserted, cannot be withdrawn until the gripping mechanism is mad e to disengage the pin, or more particularly, a groove in the pin. As a result, unauthorized removal of the tag from an article by, for example, a thief, cannot be readily accomplished.
FIGS. 5 and 6 illustrate the gripping mechanism 34 of a typical antitheft device. Gripping mechanism 34 is located in nipple 38 of disk or wafer 36 and includes both a collar 40, and a core 42. Collar 40 is secured to the interior of the base portion of nipple 38 and has a conical inner surface 44. Core 42 is located within nipple 38 and has an outer conical surface 46 that is urged upward into contact with the inner conical surface 44 of collar 40 by spring 48.
A vertical bore 50 is formed in core 42 and receives the shaft of tapered pin 54 when pin 54 is inserted into nipple 38. A horizontal bore 52 is also formed in core 42 and intersects the vertical bore 50. Two ball bearings 56 and 58 are located in bore 52. When outer surface 46 of core 42 engages the interior surface 44 of collar 40, surface 44 blocks the open ends of bore 52, causing ball bearings 56 and 58 to be wholly contained within bore 52. The size of ball bearings 56 and 58 is sufficiently large to extend into vertical bore 50 and to engage one of the grooves 60 of pin 54 when the pin is located in nipple 38.
Before pin 54 is inserted into nipple 38, core 42 is in the position illustrated in FIG. 5 and ball bearings 56 and 58 extend into bore 50. When pin 54 is first inserted into nipple 38, its tapered front end contacts balls 56 and 58 and urges core 42 downward against the force of spring 48. As core 42 moves downward, ball bearings 56 and 58 are permitted to slide radially outward from the shaft of pin 54 due to the conical shape of the interior surface of collar 40. Core 42 continues moving downward until the distance between ball bearings 56 and 58 is equal to the diameter of the shaft of pin 54. At this point, pin 54 is free to move into nipple 38. As a result of the foregoing, pin 54 is free to slide into nipple 38 at the user's discretion.
Once pin 54 has been placed in nipple 38, it cannot be removed therefrom without the use of a decoupler such as magnetic decoupler 10 of the present invention. If any attempt is made to remove pin 54 from nipple 38, the shaft of pin 54 moves slightly upward until ball bearings 56 and 58 engage any one of the grooves 60 formed by pin 54. Once this has occurred, the ball bearings 56 and 58 are forced into groove 60 by the inner conical surface of collar 40 and prevent the further removal of pin 54. Accordingly, pin 54, and along with it disk 36, cannot be removed from the article, for example, by a potential thief.
In order to unlock the disk 36 and permit the removal of pin 54, nipple 38 is inserted into a cavity of a magnetic decoupler having magnetic field in the cavity that pulls core 42 downward against the forces of spring 48 until the open ends of bore 52 are no longer blocked by collar 40, as illustrated in FIG. 6. As a result, the ball bearings 56 and 58 are free to move outward from vertical bore 50 in response to an upward tug on pin 54, allowing the pin 54 to be easily removed from the disk 36.
What is needed, then, is an improved magnetic decoupler that provides for removal of the antitheft device by a sales clerk or the like when the, article is purchased. The magnetic decoupler should include a cavity into which the nipple is inserted, and a permanent magnet structure of suitable design that provides a strong, highly focused, substantially vertical magnetic field in the cavity. The axial magnetic field gradient within the cavity should force the gripping mechanism in the nipple to disengage from the groove, allowing removal of the pin from the tag.